1. Field of the Invention
This invention relates to an image recording apparatus having a recording drum rotatable with a recording medium mounted peripherally thereof, and a recording head for recording images on the recording medium mounted on the recording drum.
2. Description of the Related Art
Such an image recording apparatus, generally, employs a construction to position and mount a recording medium such as a printing plate on the peripheral surface of the recording drum by using positioning pins and clamps (see Japanese Unexamined Patent Publication No. 2001-75292, for example). In order to check whether the recording medium such as a printing plate is positioned accurately on the peripheral surface of the recording drum, the image recording apparatus detects an edge of the recording medium by means of sensors arranged in positions opposed to the recording drum.
The position of an edge of the recording medium on the peripheral surface of the recording drum is variable with the material and reflectance of the recording medium or the presence or absence or the type of positioning holes formed in the recording medium. Thus, the edge of the recording medium cannot be detected unless the active range of the sensors is enlarged to acquire edge detection signals from the recording medium over a relatively large range. However, the sensors tend to malfunction when edge detection signals are acquired from a large range.
As noted above, the position of the edge of the recording medium on the peripheral surface of the recording drum is variable with the material and reflectance of the recording medium or the presence or absence or the type of positioning holes formed in the recording medium. Consequently, even when the edge of recording medium is placed in a correct position, the edge could be determined improperly positioned.